Method and means for inductively heating the metallic parts of inclosed electrical devices



METALLIC July 3, 1928.

A. RAVA UCTIVELY HEATING THE ED ELECTRICAL DEVICES METHOD AND MEANS FORIND PARTS OF INCLOS Filed May 29, 1924 14/ Xafid INVENTOR.

n N m T T A Patented July 3, 1928.-

ALEXANDER RAVA, OF NEW YORK, N.

Y., ASSIGN OR TO STEWART-WARNER SPEEDOI- ETER CORPORATION, OFCHICAGO,ILLINOIS, A CORPORATION OF VIRGINIA.

METHOD AND MEANS FOR INDUCTIVELY HEATING INCLOSED ELECTRICAL DEVICES.

A Application filed May 29,

The present invention relates to methods of inductively heating themetal parts inclosed within the bulb or envelope of an electrical deviceand to means for effectuating such inductive heating.

It has been proposed frequently to vaporize metallic and other gettersfor the purpose of cleaning up the residual gases within the bulb where,as, for example, in a radio vacuum tube, a high vacuum is desirable andit is immaterial whether or not the glass walls remain transparent. Thisindeed is the common practice at the present day in the manufacture ofhigh vacuum devices that depend on electronic discharge. It has alsobeen proposed to introduce a gas filling within the bulbs of rectifiers,detectors of certain types and other devices of like nature. Again gasesthat react with oxygen have been introduced into devices that areprovided with electrodes or other metal parts within the bulb either ina vacuum or in an atmosphere of gas, for the purpose of preventing theoxidization of the metallic parts. It has also been suggested that anitrogen atmosphere may be created within the envelope or bulb, as in agas filled incandescent lamp, by vaporizing nitrogen bearing compounds,as, for example, hosphorous nitride, after sealing of the ulb. It isalso a frequent practice in the radio vacuum tube art to heat theelectrodes to drive out the occluded gases from the metal duringexhaustion of the, bulb.

There has never been suggested, however, any entirely satisfactorymethod of vaporizing these substances or heating the-electrodes at adesired time. In the case of radio vacuum tubes magnesium forexample iscommonly vaporized within the envelopeby bombardment while the tube isbeing exhausted or, by inductive heating while the tube is still on thepumps. The heating of the metal parts, either inductively or bybombardment is primarily for the purpose of driving out the occludedgases. In neither instance is it possible to control the time at whichthe vaporization shall take place as it occurs whenever the temperatureof the metal parts has been raised to the vaporization point of thematerial that is desired to be volatilized. This vaporization point isgenerally a low temperature yet the THE METALLIC PARTS OF REISSUED JAN 1I940 getter should not be vaporized unti the occluded gases have beendriven out of the metal parts, an operation that requires a very muchhigher temperature.

It is the object of the present invention to provide a method and meansfor inductive heating of the metal parts of electrical devices inclosedin an'envelope, whereby the occluded gases are driven off from the metalparts by one heating, and vaporizable material, such as metallic gettersfor example, or other gas producing materials, will be volatilized byanother.

In accordance with my invention, '1 make use of the principle embodiedin F aradays law. The high frequency magnetic flux employed in inductiveheating is produced generally by a cylindrical ,coil, through which astrong current of several hundred lnlocycles is passed. The direction ofthe main flux in the space surrounded by the coil and in the immediateexternal proximity thereto is parallel to the geometrical axis of thecoil. If, now, a closed flat conducting contour or loop is placed in thepath of the flux so that the plane of the contour or loop isperpendicular to the direction of the flux, a powerful electromotiveforce is induced in the loop. This electromotive force is directlyproportionate to the size of the surface inclosed by the contour of theloop. If, however, the contour is parallel to the flux the inducedelectromotive force will be negligible.

1924. Serial No. 716,632.

In accordance with my invention, I weld upon the metal part which to beheated, a loop of conductive material in such position as may be desiredto carry out the objects of this invention.

This loop may present a completely inclosed contour in itself, or it maybe so attached to a metal part, as, for example, the grid of a radiovacuum tube, that the inclosed contour-will be formed partly by the loopand partly by the coil of the grid to which it is attached.

The accompanying drawings show the use of my invention to one particularform of apparatus to which it is applicable, namely, a radio vacuumtube. Figure 1 shows the method of using it for the purpose of drivingout the occluded gases from the grid of th tube. Figure 2 shows theapplication of of the device it will be observed that l have shown awell known type of radio vacuum g tube in which the grid, A, is ofelliptical COll construction. The plate electrode, B, is

also of the equally familiar box construction.

I have found by actual experiment that such a structure presentsconsiderable obstacles to the degasification of the electrodes byinductive heating. It has been found n fact that when vacumn tubeshaving a grid and filament electrodes enclosed within a plateelectrode'have been inductively heated to remove the gases therefrom,they differ widely in their behavior, showing iii general a lowelectronic emission and poor amplifying properties. This is particularlyso when they are used as high frequency amplifie'rs. I have discoveredthat these defects .are due to an insufficient degasification of thegrid electrode, the bars and supports of which, being shielded by thesurrounding plate, cannot be degasified properly by the present methodof inductive heating. It is also particularly the case that in thepresent methods of inductive heating, the getter is volatilized too soonand if the heating is such volatilization more gases are driven out ofthe metal parts which can no longer be counteracted by the getter andsuch gases therefore remain free within the bulb unless the exhaustpumps succeed in removing them.

By Faradays, law, the loop formed as above described when its plane isperpendicular to the direction of the magnetic flux from the ,highfrequency coil, will cause a thorough heating of the part to which it isattached. In Figure 1 it will be observed that the loop, C, is mountedon the supports D and D" which may be extensions of the grid supports.The shape of the loop, however, is such that it extends outward fromthese supports over the plate the contour of which it in part followsbut from which it is insulated. The plane of this loop is parallel tothe plane of the lateral section of the plate. The loop so mounted doesnot present in itself a closed contour since it is open at one side. Thehalf of the coils of the grid at the open side of the loop, however,complete the contour so that the same is effectively closed. When thehigh frecontinued after quency coil is brought down over the bulb of thepart in the processes of such heating as well known at the present time.But it. will also induce a current in the grid which will produce asimilar heating of that electrode. If the loop were absent, this resultwould be prevented by the shielding effect of the plate. The loop,however, overcomes this shielding effect by reason of the fact that thehigh frequency coil induces a current in the grid by reason of the factthat the rid itself forms part of the closed contour of the loop. Thecurrent is, therefore, set up with equal effect in the grid and theplate simultaneously, and the result is an equal heating anddegasification of both.

In Figure 2 it will be observed that the loop, instead of being mountedin a plane parallel to the plane of the lateral section of the plate, ismounted in a plane which is perpendicular thereto. This loop forms initself a closed contour and is welded to the plate B at the point 1).Upon the loop so mounted a small piece of metallic getter,

or other material that it is desired to vaporthe high frequency coil isapplied over the bulb in a tube to which the loop has been mounted inthis position the electrodes become heated while the loop itself remainscomparatively cool and far below the vaporization point of theattachedmaterial, and the electrodes are thus degasitied while the metallicgetter remains unvolatilized. Now, the degasification of the electrodesbeing completed, the high frequency coil may be removed and presented tothe tube a second time in such a direction that the plane of the loop,C, is perpendicular to the direction of the flux of the coil and in thiscase the loop becomes heat-ed while the electrodes remain comparativelycool. The result then is the volatilization of the getter at a time whenit is possible for it to react with all the gases driven out of theelectrodes.

It will be evident that one or more loops may be attached to the metalparts of such electrical devices, the loops being set at various anglesto the plane of the lateral section to which it is attached as shown inFig. 3. In this form of the invention one loop 0 is mounted upon thegrid electrode supports D, similar to the arrangement shown in Fig. 1,and a second loop C is mounted upon the plate electrode support D suchthat the plane of loop C is disposed at an angle to the plane of loop C.By ar ranging the loops G and G in this manner they are individuallysusceptible to magntic fields of different directions. Preferably theloop C carries a globule E of vapprizablev material to be used as agetter.

Having thus I claim is: I

1. The method of removing gas from adescribed my invention whatconductive body inclosed within an envelope wherein said body isshielded by another conductive body from a magnetic field which consistsin afiixing to said first mentioned body a loop of conductive materialforming a closed. contour with said body and being insulated from otherconductive bodies within said envelope heating said loop and saidconductive body by a high frequency magnetic field; to remove the gastherefrom, removing said gas from said envelope and sealing saidenvelope;

2. The method of degasifying conductive bodies shielded by otherconductive bodies within an envelope which consists in attaching a loopof conductive material to the body attached to a conductive to bedegasified in such manner that the loop and said body combine to form aclosed contour, said loop being insulated from the other conductivebodies within said envelope, heating said loop and the body to bedegasified by perpendicular to the plane of said loop, and cuts the loopbeyond the shielding in uence of the other conductive bodies removingthe gases from said conductive body b such heatlng, removing such gasesfrom t e envelope and sealing said envelope.

3. Themethod of degasifying the grid electrodes of radio vacuum tubes,having a plurality of inclosed electrodes including agrid inclosedwithin a plate electrode, all inclosed within an envelope, whichconsists in attaching to the (grid supports a loop so shaped as to extenoutward following in part the contour of the edge of the plate andforming with the portions of the grid opposite said loop a closedcontour, heating said loop and said grid by a high frequency magneticfield to remove the gas moving said gas from sealing said envelope.

4. The method of vaporizing substances body inclosed within an envelopewhich consists in forming said envelope, and

said condiictive body into a loop, having a closed contour, and heatingsaid'loop and said substance to the vaporization temperature of saidsubstance, by a high frequency magnetic field.

5. The method of preparing electrical dis- 7 charge devices havingconductive bodies inclosed within an envelope which consists in afiixingto one of said conductive bodies a loop having a closed contour lying ina plane transverse to the axis of said conductive body and attaching tosaid loop a vaporizable substance, then heating the conductive bodies bya high frequency magnetic field to remove the gas therefrom while saidloop remains relatively cool, afterwards heating said loop by a highfrequency magnetic field to the vaporization point of the substanceattached thereto while the said the action of a high frequency magneticfield, the magnetic flux of which is therefrom, re-' conductive bodyremains relatively cool, removing the gases from said envelope andsealing said envelope. 3

6. The method of preparing radio vacuum tubes having a plurality ofelectrodes inclosed within an envelope, some of which electrodes areshielded from the action of a magnetic field by other electrodes, whichconsists in attaching to one of said shielded electrodes a loop ofconductive material which forms with the combination of the part towhich it is attached a closed contour, heating said loop and saidshielded electrode by a high fr uency magnetic field to drive out theoccliigled gases from said shielded electrode, removing said gases fromsaid envelope and sealing said envelope.

7. The method of improving the vacuum within the envelope'of anelectrical discharge device having conductive bodies inclosed withinsaid envelope which consists in attaching to one of said electrodes aloop of conductive material in a plane perpendicular to the plane of alateral section of said the vaporization temperature of the getter,

then heating the loop by a high frequency magneic field to thevaporization point of said getter while the electrodes are at atemperature below said vaporization point, removing the residual gasesfrom the envelope and sealing said envelope.

8. The method of reparing electrical discharge devices having electrodesinclosed within an envelope which consists in attaching a vaporizablesubstance to a loop which is 'aflixed to one of the electrodes byinductive heating, driving out from the electrodes the occluded gasesthen vaporizing said vaporizable substances by inductive heating,removing the residual gases from said envelope and sealing saidenvelope.

9. The method of preparing electrical discharge devices havingelectrodes inclosed within an envelope which consists in attaching avaporizable substance to a 100 which is affixed to one of theelectrodes. then by the action of a. high frequency magnetic field,driving out from the electrodes the occluded gases and vaporizing thesaid vaporizable substances at different times, removing residual gasesfrom said envelope and sealing said envelope.

10. The method of preparing electrical discharge devices having metalparts inclosed within an envelope which consists in inductively heatingsaid metal parts to remove the gases therefrom and later vaporizing agetter afiixed to one of said metal parts, removing the residual gasfrom said envelope and sealing said envelope.

Inn

11. In an electrical discharge device havng conductive bodies sealedwithin an envelope, one of said conductive bodies being shielded fromthe influence of a magnetic flux by another of said conductive bodies,an exposed loop having an effectively closed contour attached to saidshielded conductive body which is desired to be heated inductively.

12. In an electrical discharge device having conductive bodies sealedwithin an envelope, one of said conductive bodies being shielded fromthe influence of a magnetic flux by another of said conductive bodies,an exposed loop of conductive material attached to said shieldedconductive body which is desired to be heated inductively, said loopforming in combination with the part to which it is attached a closedcontour.

13. In an electrical discharge device having conductive bodies sealedwithin an envelope a loop of conductive material having a closed contourto which is aflixed a substance to be vaporized, said loop being in aplaneparallel to the axis of said conductive bodies.

14. In a radio vacuum tube having a filament and grid inclosed within aplate electrode, all of said electrodes being inclosed within anenvelope, a loop of conductive material having a closed contour attachedto the grid supports, said loop lying in a plane parallel to the axis ofsaid grid.

15.' In a radio vacuum tube having a filament and grid inclosed Within aplate, all

of said electrodes being inclosed within an envelo e, and said gridbeing shielded by the plate rom the influence of a magnetic fiux,

an exposed loop of conductive material attached to the grid supports andforming with one side of the grid a closed contour.

16. In an electrical discharge device having elecrodes inclosed withinan envelope, one of the electrodes being shielded by another electrodefrom the influence of a magond mentioned loopihaving a closed contourand being disposed so as to be susceptible to the influence of a secondmagnetic flux disposed at an angle to the first mentioned flux.

In witness whereof, I hereunto subscribe any name this 8th day of May,1924.

ALEXANDER RAVA.

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